Physics 4.4 (Waves) Flashcards
How do waves transfer energy and what is the difference between longitudinal and transverse waves?
-Waves transfer energy from one place to another without transferring matter
-Longitudinal waves vibrate parallel to their direction of travel and examples are sound waves and P waves
-Transverse waves vibrate perpendicular to their direction of travel and examples are electromagnetic waves
What are the wavelengths of EM radiation?
-Radio: >10^3m
-Microwave: >10^-2m
-Infrared radiation: >10^-5m
-Visible light: >10^-6m
-Ultraviolet: >10^-8m
-X-rays: >10^-10m
-Gamma rays: >10^-12m
Draw a circuit to show how x-rays can be produced?
-X-rays are produced by firing high energy electrons at a copper anode
What are progressive waves?
-Waves that transfer energy away from a light source
What are two ways we can display a wave
-As a snapshot of the wave profile as the disturbance moves outwards with distance against displacement
-The oscillation of an individual particle with time against displacement
What is wavelength, period and frequency of a wave?
-Wavelength is the distance between two adjacent identical points on the oscillation, measured in meters
-Period is the amount of time it takes to complete one pattern of oscillation at any point, measured in seconds
-Frequency is the number of oscillations per unit of time, measured in hertz one oscillation per second
What is the amplitude of a wave?
-Amplitude is the distance between the rest position and a peak or trough
What is the phase difference of a wave?
-If two waves have the exact same pattern of oscillation they are said to be in phase.
-Phase difference is the shortest difference between two points on diffferent waves that are in phase
-It can be measured in degrees with 180 degrees representing half a wave or in pie with pie being half a wave and 2 pie as in phase.
What is the wave equation and the speed of light and sound?
-V=fλ
-Speed of light= 3*10^8 m/s
-Speed of sound= 340m/s
What is the equation for the intensity of a wave? and how is amplitude proportional to intensity?
Intensity=power/area
Intensity is proportional to the square of amplitude for a progressive wave
What does the distance between the wavefronts represent in a wavefront diagram?
-Wavelength
When is a wave refracted and what can be observed?
-When a wave moves from one material to another which has different optical densities
-The wave will change its speed and if the wave doesn’t pass into the object perpendicular to its surface you will notice a change in the direction
What is the equation for Snells law?
How can you determine the refractive index of a material?
1.Place a semi circular block on a piece of paper and trace around it, use a light ray to point a beam of light at the block
2.Trace the rays at different angles of incidences to the normal and use a protractor to find both angle of incidence and angle of refraction (θ₁ and θ₂)
3. Draw a graph of Sin θ₁ on Y-axis and Sin θ₂ on x-axis
What is the refactive index of air and glass?
Air:1
Glass:1.5
What is the diffraction of a wave?
-The spreading out of a wave after passing around an obstacle or through a gap, when the gap width is the same size as the wavelength of the wave
What is interference?
-When two or more diffracted wave patterns overlap and interfere with each other creating an interference pattern
What are the properties of electromagnetic radiation?
-Can all travel through a vacuum
-Have both a magnetic and electrical wave at right angles to each other
-Travel at the speed of light
-Can all be reflected, refracted, and diffracted
-Can all Demonstrate interference
-Can all be polarised
What is ionising radiation and what are the different types of ultraviolets?
-Ultraviolet, x-rays and gamma radiation are all ionising radiation this is because they have the photon energy to knock electrons from the shells of atoms.
-Ultraviolet has three types: ultraviolet A (causes tanning), ultraviolet B (causes damage such a sunburn and skin cancer) and ultraviolet C (filtered out by atmosphere) and are all emitted by the sun
What is an unpolarised wave, a plane polarised wave and a polarising filter?
-An unpolarised wave can have an electric field in any number of planes
-A plane-polarised wave is a wave that has fields in only one plane
-A polarising filter causes an unpolarised wave to have oscillating waves in only one plane
(Exam Question) Describe how you can demonstrate in a laboratory that reflected light is plane-polarised?(2marks)
-Use a polaroid/polarising filter (1mark)
-Rotate the filter and the reflected light should change intensity (1mark)
What will happen if you have a source of light and a polarising filter infront of it and then you rotate another polarising filter through 360 degrees?
-As the second filter is rotated from 0-90 degrees the light intensity decreases until it reaches 90 degrees where no light will be able to pass through light intensity then increases back up to 180 degrees
-This is because the second polarising filter is decreasing the amplitude of the wave when it rotates.
What is the equation for refractive index?
n= speed of light in vacuum/speed of light in material
How do polarising glasses cut out glare?
-Light that has been reflected can be partially polarised, more light in the direction of oscillation than other directions, polarising glasses can cut out this light reducing glare